1. Field of the Invention
The present invention relates to a connector for electrical connection. In particular, the present invention relates to a round connector that basically has a cylindrical shape and that has a circular engagement section. For example, the round connector is structured so that first connecting device is composed of a receptacle and the second connecting device is composed of a plug.
2. Related Art
One of known round connectors is, for example, a connector having a rotation guide in which an external cylinder (so-called coupling ring) is turned to guide an engagement operation. A receptacle is structured so that an outer circumference face at an end includes a male thread and a rotation ring that includes a female thread engageable with this male thread is attached to an outer circumference of a plug. When the rotation ring is rotated while the receptacle is being opposed to the plug, the male thread is engaged with the female thread to allow the receptacle to be in the vicinity of the plug, thereby providing electrical and mechanical connections between the receptacle and the plug. When the rotation ring is rotated in an opposite direction, the receptacle is away from the plug connector, thereby cancelling the electrical and mechanical connections.
The above-described connector having a rotation guide providing connection by a screw is structured to provide the connection and separation by rotating the rotation ring. However, this connector has a problem in that an insufficient connection may be caused because only the rotation of the rotation ring cannot sufficiently tell a user the connection status. Japanese Unexamined Patent Application Publication No. 6-302356 (hereinafter referred to as Patent Document 1) discloses a connector having a rotation guide by which an electrical connection status may be clearly shown and an insufficient connection status is suppressed from being caused.
The connector having a rotation guide according to Patent Document 1 is designed so that an external cylinder is turned to provide an engagement between a positioning projection and a guide groove to cause a charger-side plug to be adjacent to a storage battery-receptacle while the external cylinder and the inner cylinder being locked with a predetermined positional relation by a plurality of grooves and a plunger mechanism. According to Patent Document 1, this positional relation provides the locking position corresponding to a connection status between power source terminals and signal terminals in the plug and the receptacle, thus showing the connection status of the terminal by the rotation status seen from the exterior.
FIG. 12 is an external perspective view illustrating a charger-side plug using the connector having a rotation guide according to Patent Document 1. FIG. 12 of this application corresponds to FIG. 1 of Patent Document 1. FIG. 13 is an external perspective view illustrating a capacitor-side receptacle according to Patent Document 1. FIG. 13 of this application corresponds to FIG. 2 of Patent Document 1.
In FIG. 12, the charger-side plug 80 is structured so that an outer circumference of a columnar inner cylinder 81 is attached with an external cylinder 82 having a cylindrical shape such that the external cylinder 82 is rotatable and cannot be moved in the longitudinal direction. The inner cylinder 81 is structured so that one end-side opening includes power source terminals 81a and 81b for supplying power for charging and signal terminals 82aand 82b for transmitting charging-related information. The plug 80 is provided so that the power source terminals 81a and 81b are slightly longer than the signal terminals 82a and 82b. The other end of the inner cylinder 81 includes therein an electric wire extending while being connected to the power source terminals 81a and 81b and the signal terminals 82a and 82b. 
A rear end of the inner cylinder 81 at which the electric wire extends constitutes a grip section 83. The outer circumference of the inner cylinder 81 including the grip section 83 includes three circular grooves 84a to 84c arranged in the axis line direction. The external cylinder 82 is provided at the periphery of the front end of the inner cylinder 81. The inner circumference face of this front end-side includes a helical guide groove 821 in which one end is opened at the front end of the external cylinder 82. The guide groove 821 is formed within a range of substantially 90 degrees and this pitch of 90 degrees is a length required for the mutual disconnection of the connectors.
The rear end of the external cylinder 82 includes a finger section 823 extruding outward. The finger section 823 includes therein a plunger mechanism 822. The plunger mechanism 822 is composed of: a tube section that is provided in the finger section 823 in the diameter direction and that communicates with the inner circumference face; a ball stored in the tube section; and a compression coil spring that is provided in the tube section to bias the ball to the inner circumference face (hereinafter referred to as spring). The ball has a diameter that is slightly smaller than the inner diameter of the tube section and that allows the ball to be locked with the grooves 84a to 84c. 
At the middle of the external cylinder 82, a groove-like spring rail groove (not shown) is provided at the semicircle part of the lower surface. The spring rail groove stores therein the spring. One end of the spring is fixed to one end of the spring rail groove via a screw and the other end of the spring is fixed to the lowest surface of the inner cylinder 81 via a screw. On the other hand, the inner cylinder 81-side includes a rotation-regulating groove (not shown) formed for a range of about 90 degrees and the external cylinder 82 correspondingly includes a rotation-suppressing pin 826 having a tip end inserted into the rotation-regulating groove. The rotation-suppressing pin 826 can be rotated in the rotation-regulating groove in a range within which the spring expands and contracts in the spring rail groove in a range of 90 degrees.
In FIG. 13, a storage battery-side receptacle 90 is composed of: a flat plate-like saddle 91; and a terminal section 92 protruding from the saddle 91. The opening of the terminal section 92 includes power source terminals 91a and 91b and signal terminals 92a and 92b at positions opposed to the power source terminals 81a and 81b and the signal terminals 82a and 82b (see FIG. 9). The receptacle 90 is provided so that the power source terminals 91a and 91b are slightly longer than the signal terminals 92a and 92b. 
At the peripheral edge of the terminal section 92, a cylindrical hood section 93 is formed. The hood section 93 surrounds the power source terminals 91a and 91b and the signal terminals 92a and 92b and protrudes so as to be opposed to the inner cylinder 910. At the upper side of the hood section 93, a positioning projection 921 is formed that can be inserted into the guide groove 821. The upper side of the saddle 91 is attached with a watertight cap 95 that is provided in a rotatable manner and that covers the opening of the hood section 93.
The connector having a rotation guide according to Patent Document 1 is structured so that the plug and the receptacle are attached to each other and detached from each other by rotating the coupling ring in forward and reverse directions. The plug and the receptacle can be in adjacent to each other in the axial direction to be engaged (or connected) to provide an easy and convenient connection quicker than the conventional rotation operation. For example, this structure also may be considered as the one in which whether the plug is correctly connected to the receptacle or not is confirmed by a click feeling during the engagement.
On the other hand, a structure in which the rotation of the coupling ring is followed by an operation for moving the plug and the receptacle so that they are away from each other also can secure, after the mutual signal terminals are disengaged and before the mutual power source terminals are disengaged, a time required for turning OFF the power source. This structure prevents, when the mutual power source terminals are disengaged, spark from being caused, thus preventing the power source terminal from deteriorating. Due to the situation as described above, such a connector having a rotation guide has been desired in which a plug and a receptacle are adjacent to each other in the axial direction and are connected to each other and a coupling ring is rotated to move the plug and the receptacle away from each other. It is an objective of the present invention to provide such a connector having a rotation guide.